Small-sized, light weight, high energy density and repeatedly chargeable and dischargeable lithium ion secondary cells and other electrochemical devices are rapidly growing in demand due to their properties. Lithium ion secondary cells are relatively large in energy density, so are being utilized in mobile phones, notebook personal computers, electric vehicles, and other fields.
These electrochemical devices are being required to be made lower in resistance, higher in capacity, better in mechanical properties and productivity, and otherwise improved more along with the expansion and growth in applications. In view of this situation, higher productivity methods of production are being sought for electrochemical device electrodes as well. Various improvements are being made to methods of production enabling high speed shaping and materials for electrochemical device electrode which are suitable with the methods of production.
Electrochemical device electrodes are usually formed by laminating an electrode active material layer formed by bonding an electrode active material and a conductive material which is used in accordance with need which by a binder on a current collector. As a method for forming such an electrode active material layer, Patent Documents 1 and 2 disclose a method of spray drying a slurry which contains an electrode active material, rubber particles, and dispersant to obtain a particle-shaped electrode material and using the obtained electrode material to form an electrode active material layer.
However, in the art described in Patent Document 1, when preparing a slurry, no viscosity adjuster is used, so the viscosity of the slurry is low, the binder ends up concentrating locally at the surface in the particle-shaped electrode material, the obtained particle-shaped electrode material becomes inferior in fluidity, and therefore an electrode which has a uniform film thickness cannot be fabricated. Further, in the art described in Patent Document 2, carboxymethylcellulose is used as a viscosity adjuster which acts also as a dispersant, but carboxymethylcellulose bonds with the binder in the particle-shaped electrode material. Due to this, the binder ends up becoming hard and the adhesion with the current collector sometimes becomes insufficient when press-forming the obtained particle-shaped electrode material.
Further, development work is proceeding on the active material for positive electrode for the purpose of raising the performance of lithium ion secondary cells. Attention is focusing on an active material for positive electrode which contains nickel or another transition metal for the purpose of raising the capacity. Such an active material for positive electrode for raising the capacity exhibits a strong basicity due to the lithium carbonate which was used at the time of production of the active material remaining in the active material. For this reason, as in the art described in Patent Documents 1 and 2, when using the active material for positive electrode to obtain an aqueous slurry and spray drying the obtained aqueous slurry, the strong basicity causes the spray drying apparatus and other production equipment to end up corroding. Due to this, the aqueous slurry ends up being contaminated by foreign matter. When making an electrode, there were the problems that the cycle characteristics and other cell characteristics ended up falling.